1912] Icebergs and their Location in Naviriation. rr23 



WEEKLY EVENING MEETING, 

 Friday, May 31, 1912. 



Donald William Charles Hood, Esq., C.V.O. M.D. F.R.C.P., 



Vice-President, in the Chair. 



Professor Howard T. Barnes, D.Sc. F.R.S. 

 Icebergs and their Location in Navigation. 



Origin of the North Atlantic Ice. 



The icebergs met with in the North Atlantic each year are almost 

 entirely derived from Western Greenland. The interior of Greenland 

 is covered by a large ice-slieet forming an enormous glacier, which 

 gradually moves outwards, meeting on its journey mountains and 

 islands which form a fringe of varying width. This mountainous 

 belt is penetrated by deep fiords, through which the ice passes 

 towards the sea. As the huge ice-sheets are forced into the sea they 

 are broken off and set adrift as bergs. The ''■calving,'" as it is 

 called, may take place in a number of ways. 



Von Drygalski distinguishes three classes of bergs ; those of the 

 first class are the most massive of all, and separate with a sound like 

 thunder from the entire thickness of the glacier front. They result 

 from the buoyant action of the water as the glacier pushes out into 

 the deep water. They usually regain their equilibrium after rhythmic 

 oscillation, and float away in an upright position. Bergs of the 

 second class are broken off under water from time to time. They 

 rise and often turn over before they gain equilibrium, displaying in 

 this way the beautiful blue colour of the lowest layers of ice. Bergs 

 of the third class form almost continuously, and consist of large 

 and small fragments which separate along the crevasses and fall into 

 the sea. 



The size of the pieces of ice set adrift varies very much ; but 

 bergs 60 to lOO feet to the top of their walls, with spires and pinnacles 

 from 2u0 to 250 feet high, are most often found. The length of 

 sucli an average berg would be from ;!00 to 500 yards. The depth 

 of these masses under water is variously given as from seven to 

 eight times the height, but this is not always the case. It is possible 

 to have a berg as high out of the water as it is deep below the 

 surface, since the submergence depends entirely on mass and not on 

 height. It is possible to find bergs with a pinnacle rising high out 

 of the water, but offering little weight to the mass below. The 

 highest berg in the Arctic which has been recorded had pinnacles 

 1500 feet high. Bergs are produced all the year round throughout 



